Measurable far-field effects attributable to salmon aquaculture (increased sedimentation, nutrient enrichment/eutrophication and effects on food web structure/function) have been observed at the ecosystem level in some marine coastal locations in Canada. The ESSA project uses modelling and observations of sensitive variables to assess and predict these habitat alterations. Particulate matter released settles rapidly under and near cage sites, but potential exists for horizontal transport and widespread dispersion, particularly in areas with high currents. Finite element modelling, multibeam imaging, direct measurements of sedimentation and estimates of sediment accumulation rates identify depocenters and show the extent to which lateral transport increases sedimentation proximate and distant from farm sites. Mass balance models are used to evaluate rates of organic matter and nutrient loading relative to inputs from aquaculture sites. Levels of nutrient enrichment reflect the scale of aquaculture, local hydrographic characteristics and the magnitude of other sources relative to inputs from cultured fish. Changes in benthic infauna (decreased diversity, predominance of sulfide-tolerant 'indicator' groups) reflecting higher rates of organic matter sedimentation and sediment oxygen depletion have been detected over distances >200 m.